DE3151831A1 - METHOD FOR DETERMINING AN ABNORMAL STATE IN A ROBOT CONTROLLER - Google Patents

Description

j NACHOEREI OHTJ

6 / 4-53 FUITSU FANUC LIMITED

Method for determining an abnormal condition in a robot controller

Priority: December 30, 1980 Japan 186751 Background of the invention

The invention relates to a method for determining an abnormal condition in a robot controller. In detail The invention relates to a method for improving safe operation when an abnormal one is detected State, for example one. Overload during robot operation

The rising labor costs in the industrialized world have led to an increasing need for labor saving Measures and improvements in manufacturing processes. Industrial robots are used to meet these requirements have been put into use and have proven to be very successful. Mainly excellent Achieve results in factories with numerous machine tools using industrial robots be able to carry out simple tasks such as changing workpieces and tools on the respective machine tools. The demand for such robots is growing every year. These industrial robots have a so-called "play-back" or memory ability. With their help, the robots are taught their tasks or services and then cause these tasks to be carried out if necessary. In detail, a teaching device is provided for this purpose enter the tasks to be performed, these tasks

ben consist of robot instruction data previously stored in a memory within an associated control unit were saved. As soon as the request for a special service on the part of the machine tool is received, a series of robot instruction data is sequentially read out from the memory, and the robot responds to the instructions by operating the machine tool as often as necessary.

The robot instruction data includes positional information regarding the point at which the service is provided is to be carried out, the robot working speed and service signals representing an instruction such as the Hand of the robot must be controlled at the point mentioned above, and which also exchange signals with it on the machine tool side. In general, the above-mentioned teaching operation proceeds in the following manner away:

(1) Setting up the memory addresses of the memory locations, in which the sections of the robot instruction data are to be stored.

(2) Positioning the robot arm by a "jog-feed" Operation, that means manual movement of the arm.

(3) Plotting the position information under consideration of the service point and setting the value for the speed control.

(4) plague the robot service code.

A series of robot operations related to a machine tool is accomplished by repeating the foregoing Steps (1) through (4-) taught. Accordingly, as long as there is no problem with the mechanism or the control system

of the robot, and after the robot arm has been positioned at a predetermined working speed, the robot executes the robot instruction data accordingly and services such as workpiece and / or tool changes, Remove chips, manipulate by hand and the like.

However, there are cases when the robot cannot function properly or when there is an abnormality developed in the associated peripheral facilities. Such a case is given when the robot is an extreme heavy workpiece lifts or grabs or he goes about it, a workpiece together with the associated jig or it could push against the machine tool. Such events can lead to Damage the robot or the machine tool, or both. Conventional systems are not set up to to adequately solve the problems described and therefore do not offer the required level of security.

Brief summary of the invention

Accordingly, the aim of the present invention is to create a new method for robot control, which makes it possible to detect malfunctions due to overload.

It is also an object of the present invention to provide a method for detecting abnormal conditions a robot controller to avoid damaging a machine tool and the robot by stopping it immediately of the robot after detecting an overload.

Finally, it is the object of the invention to provide a method for detecting abnormal conditions in a robot controller to provide the abnormal robot operation by previously entering the magnitude of the motor current or the limit values of the motor current to determine the occur when the robot is working normally and then compare the magnitude of the motor current when the robot actually performs a task, with the value of the specified drive current or a limit value for the Comparison is used.

Another object of the invention is to provide a method for determining abnormal conditions in a robot control arrangement to find, wherein an overload condition at a predetermined robot position is checked in a simple manner by sending a drive current test instruction as part of the robot instruction data to a correct place within the instruction data should be used.

These and other objects and objects of the present invention will become apparent from the description below, which is illustrated by the accompanying drawings, in which like reference characters have the same or similar parts denote in all figures.

Brief description of the drawings

Fig. 1 shows the embodiment of an industrial robot, to which the present invention is applicable, and in which with (A) a plan view and with (B) a side view is designated and

Figures 2, 3 and 4- show block diagrams of various arrangements for carrying out the method according to the invention for detecting abnormal conditions in a robot control arrangement.

Description of a preferred embodiment

Before beginning to describe the present invention, let us consider an industrial robot on which the Invention relates, explained in more detail in connection with Fig.1. The industrial robot shown there has a mechanical hand 1 for gripping workpieces or tools that are to be replaced. One joint 2, that can be bent (<* axis) and tilted up and down can be ((2-axis) as well as an arm 3, which can be freely extended or shortened (R-axis) are also intended. 4 with a housing is referred to, which are moved vertically (Z-axis) along a shaft PL can and from one side to the other (Θ-axis) the shaft PL can be pivoted. With 5 a frame is referred to as a support of the housing, with 6 the teaching device to enter the robot movement. This has a control panel operated by an operator can be, as well as a control unit 8 for storing the entered data one after the other using the Teaching device (the data mentioned will later be referred to as instruction data), for example the work position (the point at which a particular service must be performed), the speed of work and the various services to be performed as well as signals for controlling the movement of the handset, of the joint 2. and the housing 4- in accordance with the instruction data.

To explain the invention, reference is now made to FIG taken. A robot control unit RBC, consisting of a microcomputer, serves to supply the instruction data, a control program and other such data

save and exchange signals with the machine tool side, to control the robot ·. A pulse distribution circuit PDC contains a Z-axis move command Z. from the robot control unit RBC and performs a pulse distribution operation based on the Size of Z to generate distributed impulses (hereinafter referred to as Command pulse) Z, the number of which is a function of the size of Z. The command pulses Z are fed to a reversible counter (hereinafter referred to as the error register) ERR, which additionally Receives feedback pulses FBP, which are each generated when a DC motor DMZ, which will be described later has passed through a certain angle. The ERR error register is used to match ' with the direction of the robot movement the command pulses Z and to count up or down the feedback pulses FBP. In detail, it is assumed that the robot . Moves along the Z-axis in the positive direction. In in such a case, the content of the error register ERR is counted up by one counter every time a command pulse Z was generated and this is down counted by one counter each time a feedback pulse FBP was generated. Conversely, if the Robot along the Z-axis in the negative direction, the content of the error register ERR is down by one counter counted when a control pulse Z is generated was, and .. "accordingly it is incremented by one counting unit counted when a feedback pulse FBP has been generated. The one stored in the ERR error register Information constantly represents the difference between the number of command pulses Z and the number of feedback pulses FBP. A digital / analog converter DAC receives a signal from the error register ERR, which its

Displays content and performs a digital-to-analog conversion to produce an analog position error voltage E- that is proportional to the received signal, ie proportional to the content of the error register ERR. An addition / subtraction circuit ADD generates a differential voltage. E duroh calculation of the difference · between the position error voltage E and a speed voltage E_, which is proportional to the currently prevailing speed of the DC motor DMZ. A speed control voltage VCO, which receives the difference voltage E. from the addition / subtraction circuit ADD, comprises a circuit arrangement (not shown), for example a phase compensation circuit, a thyristor phase control circuit and a thyristor circuit. This is used to control the motor speed in such a way that the differential voltage E _c goes to zero the voltage supplied to the rotational speed is regulated. The DMZ motor referred to above is a DC motor for drive along the Z-axis. This receives a regulated voltage from the speed control circuit VCC. A tachometer generator TC is coupled directly to the DC motor shaft. This produces a speed _{voltage E 5} , the amplitude of which is proportional to the respective speed of rotation of the DC motor DMZ. A sensor RE, for example a rotary encoder or decoder, generates a feedback pulse every time the DC motor has rotated a predetermined angle. A current sensor CT, for example a current transformer, determines the armature current (hereinafter referred to as the drive current

draws), which feeds the DMZ DC motor. An analog / Digital converter ADC receives the drive current value, which was determined by the current sensor CT and converts this into a digital value.

MPX is a multiplexer that receives a digital measured value from the analog / digital converter ADC. If the robot control unit RBC emits a current teaching signal CTS in the current teaching state for the operation, the multiplexer MPX sends the digital value 1 ™ ^ of the drive current at this time to the robot control unit RBC. If the robot control unit RBC sends a current test command signal CCS to the multiplexer MPX while the robot is currently performing a service, the multiplexer replies by outputting the digital values Ijv ~ of the currently flowing feed current, which is stopped while the robot service is being performed, to the comparison unit CMR, which will be described below. After receiving the digital value I _DT for the drive current from the multiplexer MPX, the robot control unit RBC processes the signal in a predetermined manner by calculating the limit values of the drive current at the time of abnormal behavior, ie the upper and lower limit values of the drive current. The robot control unit RBC stores these upper and lower limit values in a memory TCM. In detail, the memory TCM stores the upper and lower limit values I _mo ", I _ ^ _ of the permissible current. These upper and

IHcLjC III HX

lower limit values are in fixed addresses of the memory TCM inscribed by a write command WTC and read out again from fixed addresses of the memory TCM by a read command RDG. The commands RDC, WTC are output by the robot control unit RBC. If the robot test unit RBC gives the current test signal CCS during

the process of a robot service, so compares the above-mentioned comparator CMR the upper and lower limit values 3L - ,,, 3Lj ^, which are generated by the memory TCM

To ei χ mm

with the value l ^ g of the drive current, which is supplied by the multiplexer MPX, which continues for the further robot service. If it is determined that the magnitude of the drive _{current I DS is} greater than I _max or less than I _min , the comparator CMR generates an alarm signal ALM.

The mode of operation of the arrangement according to FIG. 2 is shown below described. First of all, the robot control device RBC is given the necessary robot movements and operations taught in the usual way. During this procedure, drive current test instructions are given in advance by the operator added to the instruction data in a suitable place «This is done by entering a robot service code executed, which the drive current test instruction inserts into the instruction data at a location where the drive current is to be checked as desired. Next the device is placed in the current teaching state, and the robot becomes in accordance with the instruction data actuated.

When the robot control unit RBC issues the Z-axis movement command Z, the pulse distribution circuit PDC performs a pulse distribution operation and supplies command pulses Z as described above. The error register ERR counts the command pulses Z up or down, depending on the direction of the robot movement and sends the resulting value to the digital / analog converter DAC, which converts _{this signal into the position error voltage E 3.} The position error voltage E is supplied to the DC motor DMZ via the addition / subtraction circuit ADD and the speed control circuit VCC, whereby the motor DMZ is set in motion.

- ier -

When the motor DMZ is running, the tachometer generator TG produces a voltage E_ corresponding to the respective speed, and the sensor RE generates feedback pulses whenever the direct current motor DMZ reaches a predetermined value. Has traversed an angle. The feedback pulses are input to the error register ERR, which now supplies the arithmetic difference between the distributed control command pulses Z and the feedback pulses EBP. The difference, ie the content of the error register ERR, is converted into the position error voltage E in the above-described manner. Next, the addition / subtraction circuit ADD calculates the difference voltage E _n , ie the deviation from the voltage E "for the current speed. The motor DMZ is driven by a differential voltage so that the robot moves towards the target position along the Z-axis at the commanded speed. In other words, according to the instruction data, the robot is steadily moved toward the new target position and performs the predetermined task.

When the drive current test instruction is read from the instruction data under the foregoing conditions, the robot control unit first outputs the current teaching signal CTS, whereupon it receives the digital drive current value Ijjrp via the multiplexer MPX. The robot control unit RBC then subjects this digital value I ^ m to a defined processing process in order to determine the upper and lower limit values I _max >> - ^ min ^ " ^{of the} permissible current.

These limit values are then stored in the TCM memory. The robot control unit can be set up in such a way that that these values are calculated in the following way. if the current teaching signal CTS was issued, the robot control unit receive the value of the drive current at certain times when the robot moves from a point to the next has moved and can do the top and bottom

Limit values based on the mean of the deviation of the continuously received values or based on calculate the maximum and minimum value of the current.

Thereafter, the robot operations are carried out in accordance with the instruction data and with the upper and lower Limits of the drive current at other robot positions are entered concurrently with one another, i.e. taught.

If the test instruction for the drive current is read from the instruction data during the course of a robot service in which the robot is controlled in accordance with the instruction data, the robot control unit RBC supplies the current test signal CCS and the read command RDC to the lines C ^ , I ^ Als, respectively The result of this is the predetermined upper and lower limit values I, I from the memory. supplied, and the digital values of the drive current I _DC are at predetermined 'time points by the multiplexer MPX, the values of D _m,: supplied j_ _n »D and I ₁₁ O to the comparator unit CMR, which checks whether the driving current value I ^ g greater than the upper limit value I _max or less than the lower limit value I _min . If I _{DS is} greater than I _max or less than I _n -, then the comparator CMR outputs the alarm signal ALM, whereupon the movement of the robot is stopped.

It should be noted that the description in connection with FIG. 2 relates only to the Z-axis. In practical operation, however, the control is carried out in a similar manner for the other axes (R-axis, Θ -axis). It has also been described that the upper and lower limit values are contained in the memory TCM. If an arithmetic circuit is provided on the output side of the memory TCM for the upper and lower limit value, the mean value of the drive current can also be stored in the memory TCM and thus a calculation

adjust the limit values using the arithmetic circuit. In the arrangement described above, the Memory TCM, the comparator unit CMR etc. are described as if they were outside the robot control unit RBC are arranged. However, a robot control unit RBC composed of a microcomputer can also do so can be set up to perform these functions and the upper and lower limits can be set in the instruction data is inserted.

In the arrangement described above, the upper and lower limits are obtained by reading the motor drive current while the robot is in accordance works with the instruction data. Next, an arrangement will be described in which the values of the Motor drive current in advance based on robot position and posture and load information, .for example, the workpiece weight are determined. This enables the upper and lower limit values from the set drive current value in advance.

To describe a second embodiment of the invention, reference is made below to FIG. In contrast to the first embodiment, the arrangement is such that the limit values, ie the upper limit value I _max and the lower limit value I _m 4_ _{n of} the permissible current are calculated from the robot position and posture and the weight of the workpiece and are previously stored in memory IM get saved. Specifically, in the arrangement according to FIG. 3, the limit values are calculated in advance for each of a plurality of robot positions, and the calculated values are each stored in advance in time in the memory IM. Furthermore, a drive current test instruction in the form of a service code is inserted into the robot instruction data, which corresponds to the respective robot position.

speaks. When the drive current test instruction is read then the previously determined limit values and the drive current value I ^ g are determined by the current sensor CT and fed to the comparator circuit CMR for comparing their size, which has already been mentioned in connection with FIG. 2 has been described.

In a different embodiment according to FIG. 4, it is possible to proceed with the motor power in the same way as with the motor drive current. This is a particularly effective arrangement when a DC servo motor is used as the robot drive motor, because there is a proportional relationship between the load torque and the drive power. The arrangement of Figure 4 differs from that according to Figure 3 is that a power sensor PT instead of the current sensor is provided, and in that the limit values of the Roboterlei-.stung, ie the upper limit value P _m - _V and the lower

Ul ClX *

Limit value P. the performance are contained in the memory IM. P in Fig. 4 denotes the measured power.

The invention described above makes it possible abnormal conditions, such as overload, can be detected with a high degree of certainty and a malfunction of the robot, which can lead to damage to the robot or machine tool.

Obviously there are numerous different embodiments of the invention are possible without departing from its essential essence, the invention is intended should not be seen as limited within the embodiments, without prejudice to the definition in the appended Claims.

Claims (2)

6 / 4-53 FUJITSU PANUC LIMITED Patent claims 1. Procedure for determining an abnormal condition.es in a robot control arrangement for operating a robot in accordance with instruction data by the following steps: Operation of the robot on the basis of instruction data in the teaching of limit values mode, Reading the value for the motor drive current or for the motor drive power in this operating state, Setting the calculated limit values in accordance with the value of the drive current or drive power, Determining the value for the motor drive current or for the motor drive power in the "play-back" operating mode of the robot, monitor the determined value to determine whether this is outside the range of the limit values and Generating an alarm signal if the determined value is outside the range of the limit values. 2. The method according to claim 1, characterized in that the values of the motor drive current are averaged, and that the limit values are calculated according to the mean values. 3 »Method according to claim 1, characterized in that the instruction for checking the motor drive current value is set in the instruction data, and the value for read the motor drive current as a function of the instruction data in the teaching of the limit value operating state is used to calculate the limit values that are set in response to the value of the motor drive current is read as a function of this instruction in the "play-back" operating state, in order to then display the value monitor whether it is outside the limit values. 4 ·. Procedure for controlling a robot in accordance with instruction data, characterized by the following steps: Setting the drive current value according to the robot position and position and according to the weight of a workpiece, Setting the limit values based on the Current values have been calculated, Determining the motor drive current for the robot "playback" Operation, Monitoring the determined values to determine whether these lie outside the range of the limit values and Generating an alarm signal when the determined values lie outside the range of the limit values. 5. Method according to claim 4, characterized in that that an instruction for checking the motor drive current value is set in the instruction data in advance so is that when this instruction is read a decision is made as to whether the motor drive current value is within the range of the limit values.